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30 Plymouth Electrical Problem


hursst

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Hello,

I have a 1930 Plymouth (all stock, except for modern coil) that has some electrical issues that maybe someone could help me with.

What happened was, I was driving the car to a cruise-in and noticed that my horn didn't work. I friend later told me my brake lights didn't work, and upon further inspection, neither did the lights. Turned out to be a blown fuse. When I went to restart the car about 5 hours later, the battery was dead and I had to get a push start. Once I got going, everything was fine. I replaced the fuse when I got home.

About a week later, I was going to drive the car again, and the battery was dead again. The battery is old, so I figured it was time to replace it anyway (6 volt). I bought a new battery, hooked everything up, and the car started up fine; however, the ammeter is now reading a discharge condition. I took the generator off and had it tested (it charges just fine) and I checked the current at both generator posts, at the ignition, and through the ammeter gauge, and checked the battery current, and everything read 6-6.5 volts or so. The engine seems to run fine and I was able to run it a few miles in this condition with no problems.

Does anyone have any ideas on why my ammeter would be showing discharge when I replaced the battery? I'm not very good with electrical, so maybe I'm overlooking something obvious? Thank you for any help that can be provided.

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Sounds like you have a grounding issue or maybe a wire rubbed through that is touching metal. These are always fun to fix. The battery going dead on its own is a indicator of unwanted current flow in the wiring. It would be best to disconnect the battery terminals until you get it fixed to prevent a fire.

Terry

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Yes, it sounds like a ground problem, as if there is a bare wire or frayed wire grounding somewhere.

Here is a way to find where the problem is. Take out the fuse and put a 6 volt test light in its place. With everything turned off, it should be dark. If it lights up even a little, something is drawing current. Try disconnecting the circuits one by one until you find the one that is causing the problem, the light will go out when it is disconnected.

Or, you can carefully examine the wiring for frayed or broken wires or bare wires touching or similar.

If it is not in the wiring it may be some component burned out or shorting out. Again, if you can't find anything that has stopped working or that is obviously burned out or broken, you can disconnect them one at a time.

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Guys, thanks for the help and replies. I've been testing and inspecting some wires and checked the owner's manual for the wiring diagram. According to the owner's manual, the car has the + terminal going to ground and the - terminal going to the starter. Is this what they call "negative earth?" Anyway, I turned the batttery around and hooked it up this time as the manual's electrical diagram says, with the + terminal to ground, and the car started right up and the ammeter reads as normal. I tested the battery current and it how goes into a negative voltage reading with a voltmeter, which I guess is what I would expect now with + going to ground.

Again, I'm very bad with electrics, but does this sound reasonable? I would have thought that hooking the battery up backwards would have caused some other problems in the first place, other than having the ammeter show discharge while driving. Everything appears to be working now, but I'm kind of skeptical if I did this correctly or not.

Thanks again for your knowledge on this!

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Thanks keiser31. I always learn something from you guys.

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Please clear up a couple of questions....was the battery you replaced positive post grounded? Did you reverse the battery terminals when installing the new battery? A battery with the positive going to ground would be called positive earth and of course the reverse for the negative ground. The Brits use the word earth for what we call ground, just as they call a vacuum tube a valve.

As suggested above the test lamp is your friend. It can be used no matter how the battery is hooked up. Check to make sure you have no current drain with everything off. If not, then your problem is still there and you need to trouble shoot. Good luck.

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Yes, your car has a "positive ground" system. It is a matter of complete indifference to the battery whether it is a + or - ground system, as long as it is hooked up the right way around. This was a decision made by the designer when he designed the electrical system and everything was made to suit.

It is a good thing you caught the mistake in time. Putting the battery in backwards can make some very weird problems. For example your horn will suck instead of blow (joke).

If you are lucky you did no harm. If you left it that way too long you might have ruined the battery but it seems to be ok.

Incidentally before 1955 most cars had 6v positive ground systems. All Ford products, all Chrysler products, some GM products, and I believe all the independents were that way.

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Evidently the first battery was positive post grounded and I didn't pay attention to it, assuming it was negative post-grounded. I did not reverse any terminals. I'll run some more tests to see if I can find a ground problem, but it seems to be okay. Took it for a drive today and had no problems. Thanks.

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You should have noticed if the battery cables were installed incorrectly. The + post is bigger around than the - post. It would have been difficult to put them on backwards. I think a 30 Plymouth would run either way, The generator may not charge, as it would have been polarized + ground. The coil would work, however not as efficiently. I am with Beltfed, I think there is another problem.

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You should have noticed if the battery cables were installed incorrectly. The + post is bigger around than the - post. It would have been difficult to put them on backwards. I think a 30 Plymouth would run either way, The generator may not charge, as it would have been polarized + ground. The coil would work, however not as efficiently. I am with Beltfed, I think there is another problem.

Putting a battery in backwards can cause odd problems, similar to a bad ground. On an old car it will do little harm, just turn the battery right way round. On a new car with all the electronics, I suppose you could blow thousands of $$$$$ worth of parts.

Chances are the problems were related to the backwards battery, and were solved when he fixed it.

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6-6 1/2 volts is what a new battery should read when parked. I would think you should get up to 7 when charging properly.

Take a voltage reading when the engine is running and when it is shut off and do a comparison.

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Backwards battery was the problem. I have found no other issues thus far and have been able to drive it with no additional problems. I'll continue to monitor everything and test it again next week, as I won't be driving it until then. Leaving the battery disconnected just in case...

Thanks again for everyone's excellent advice.

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Getting back to the blown fuse / flat battery, I would be looking for a bare wire chafing at the bottom of the steering column. The horn wire and lighting switch power goes through a switch fixed to the bottom of the column, this switch shares a common fuse with lights and horn.

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